Surface ozone and its precursors at Summit, Greenland: comparison between observations and model simulations

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Y. Huang, S. Wu, L. J. Kramer, D. Helmig, R. E. Honrath
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2017
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic; Greenland
• Online Access: https://doi.org/10.5194/acp-17-14661-2017; https://doaj.org/article/77f055371b104a998572562924aa3383

Recent studies have shown significant challenges for atmospheric models to simulate tropospheric ozone (O 3 ) and its precursors in the Arctic. In this study, ground-based data were combined with a global 3-D chemical transport model (GEOS-Chem) to examine the abundance and seasonal variations of O 3 and its precursors at Summit, Greenland (72.34° N, 38.29° W; 3212 m a.s.l.). Model simulations for atmospheric nitrogen oxides (NO x ), peroxyacetyl nitrate (PAN), ethane (C 2 H 6 ), propane (C 3 H 8 ), carbon monoxide (CO), and O 3 for the period July 2008–June 2010 were compared with observations. The model performed well in simulating certain species (such as CO and C 3 H 8 ), but some significant discrepancies were identified for other species and further investigated. The model generally underestimated NO x and PAN (by ∼ 50 and 30 %, respectively) for March–June. Likely contributing factors to the low bias include missing NO x and PAN emissions from snowpack chemistry in the model. At the same time, the model overestimated NO x mixing ratios by more than a factor of 2 in wintertime, with episodic NO x mixing ratios up to 15 times higher than the typical NO x levels at Summit. Further investigation showed that these simulated episodic NO x spikes were always associated with transport events from Europe, but the exact cause remained unclear. The model systematically overestimated C 2 H 6 mixing ratios by approximately 20 % relative to observations. This discrepancy can be resolved by decreasing anthropogenic C 2 H 6 emissions over Asia and the US by ∼ 20 %, from 5.4 to 4.4 Tg year −1 . GEOS-Chem was able to reproduce the seasonal variability of O 3 and its spring maximum. However, compared with observations, it underestimated surface O 3 by approximately 13 % (6.5 ppbv) from April to July. This low bias appeared to be driven by several factors including missing snowpack emissions of NO x and nitrous acid in the model, the weak simulated stratosphere-to-troposphere exchange flux of O 3 over the summit, and the ...